Biometric authentication device

ABSTRACT

A biometric authentication device of the present invention includes a light guide layer on which a light diffusion unit for displaying an aerial image representing a design of a living body at a height is formed, a light source that irradiates the light guide layer with light, a polarized beam splitter disposed on an upper surface side of the light guide layer, a retroreflective layer disposed on a bottom surface side of the light guide layer, and an imaging camera that captures an image of a living body superimposed on the aerial image through an opening formed in the retroreflective layer, and performs biometric authentication based on an image captured by an imaging camera.

BACKGROUND 1. Related Application

The present application claims priority to Japanese Patent ApplicationNumber 2022-095475, filed on Jun. 14, 2022, the entirety of which ishereby incorporated by reference.

2. Field

The present disclosure relates to a biometric authentication device witha function of displaying an image in the air using retroreflection.

3. Description of the Related Art

Aerial Imaging by retro-reflection (AIRR) is known. For example, inorder to enable observation of an image formed in the air from a widerangle, the display device of JP 2017-107165 A uses two retroreflectivemembers, and one of the retroreflective members is disposed on anemission axis of a light source. For easy adjustment of the position atwhich an image is formed, an image display device in JP 2018-81138 Aincludes a semitransparent mirror, a retroreflective member, and animage output device disposed parallel to each other. In order to inhibita reduction in the viewability of an image, an image display device inJP 2019-66833 A reduces the number of times of transmission of lightthrough a retardation member (λ/4 plate). For achievement of a reductionin device thickness, a display device in JP 2019-101055 A includes adisplay and a retroreflective member disposed parallel to a beamsplitter, and a deflecting optical element disposed on the display.

SUMMARY

In various electronic devices and electronic systems, personalauthentication using a living body such as a fingerprint or a vein hasbeen advanced. For example, in a vein authentication of the palm, a handis placed on the surface of a transparent acrylic plate, the vein of thepalm is imaged by a camera from the back surface side of the acrylicplate, and whether or not the person is the person himself/herself isauthenticated based on the imaged image.

In conventional biometric authentication, a contact authentication inwhich a hand is brought into contact with an acrylic plate is mainlyused; on the other hand, non-contact biometric authentication is alsounder development. In the contact type of authentication, since the handis placed on the acrylic plate, stable photographing of the vein by thecamera is possible. However, in the non-contact type of authentication,there are problems such as the camera not focusing because the height ofthe hand is not fixed in the air, and it takes time and effort toachieve focus.

Therefore, for example, a proposal has been made to express anappropriate position of the hand with color of illumination. FIGS. 1A to1E illustrate a schematic configuration of a biometric authenticationdevice equipped with such a function. As illustrated in FIG. 1A, animage P of the hand is lit on the surface or inside of an authenticationdevice 10, the user holds a palm H in the air to be aligned with theposition of the image P, and then the palm H is imaged by the built-incamera of the biometric authentication device 10.

FIG. 1B is a block diagram illustrating an internal configuration of thebiometric authentication device 10. The biometric authentication device10 includes a sensor 20 that measures a distance to the palm H, anillumination unit 30 that illuminates the image P with a colorcorresponding to the measured distance, a camera that images the palm H,and a control unit 50 that controls each unit. In some embodiments, thecontrol unit 50 and/or illumination unit 30 may be implemented withcircuitry, a controller, a hardwired processor, and/or a processorconfigured to execute instructions stored in a memory.

As illustrated in FIG. 1C, when the palm H is approaching the biometricauthentication device 10 (provided that, the height D1 is larger thanthe focal length of the camera 40), the control unit 50 lights the imageP in blue via the illumination unit 30 to notify that the palm H is toofar from the appropriate position. As illustrated in FIG. 1D, when aheight D2 to the palm H is that of an appropriate position(substantially matched with the focal length), the control unit 50lights the image P in green via the illumination unit 30 to notify theuser that the palm H is at the correct height. At this time, the camera40 captures an image of the palm H. As illustrated in FIG. 1E, in a casewhere a height D3 to the palm H is such that it is too close, thecontrol unit 50 lights the image P in red to notify the user that thepalm H is too close.

As described above, the conventional biometric authentication device cannotify the user of whether the height of the hand is appropriate bychanging the color in which the image P is lit. However, since the userdoes not intuitively know the appropriate height of the hand, the userstill needs to perform work such as adjusting the height of the palm Hwhile checking the lighting color of the image P, which is troublesome.

An object of the present disclosure is to solve such a conventionalproblem, and to provide a biometric authentication device in which theposition for an authentication target such as a hand or a finger is ableto be intuitively understood.

The biometric authentication device according to the present disclosureis a biometric authentication device with a function of displaying anaerial image using retroreflection, the biometric authentication deviceincluding a light guide layer on which a design for an aerial image isformed, a light source that irradiates the light guide layer with light,a polarization beam splitter disposed on one principal surface side ofthe light guide layer, a retroreflective layer disposed on a side of theother principal surface of the light guide layer, the other principalsurface facing the one principal surface, and an imaging unit thatcaptures an image of a living body in the vicinity of a region where anaerial image is displayed via an opening formed in the retroreflectivelayer, in which the biometric authentication device performs biometricauthentication based on the image captured by the imaging unit.

In one aspect, a polarization filter having a polarization directiondifferent from that of the polarization beam splitter is provided at aposition matching the opening. In one aspect, a polarization directionof the polarization filter is orthogonal to a polarization direction ofthe polarization beam splitter. In one aspect, the imaging unit capturesan image of a living body at a time when the light source is turned off.In one aspect, display of the aerial image and imaging of the imagingunit are time-divisionally controlled. In one aspect, the imaging unitincludes an infrared camera, and a visible light filter that shieldsvisible light is provided at a position matching the opening. In oneaspect, the aerial image is generated at a position symmetrical to thedesign with respect to a surface of the polarization beam splitter, anda focal point of the imaging unit is adjusted to a position of theaerial image. In one aspect, the biometric authentication device furtherincludes an output unit that notifies the user that imaging by theimaging unit has ended. In an aspect, the living body is a fingerprintor a vein.

According to the present disclosure, since the aerial image is displayedso as to guide the living body to the position where the biometrics areto be placed in the air, and the biometrics placed at the position isimaged, the user can intuitively recognize the position to which thebiometrics are held, and it is possible to eliminate troublesomebiometric authentication due to non-contact.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1E are diagrams illustrating a schematic configuration of aconventional biometric authentication device;

FIG. 2A is an external perspective view of a biometric authenticationdevice according to a first example of the present disclosure, and FIG.2B is a side view thereof;

FIG. 3 is a schematic cross-sectional view taken along line X-X of thebiometric authentication device illustrated in FIGS. 2A and 2B;

FIG. 4 is a schematic cross-sectional view of a biometric authenticationdevice according to a second example of the present disclosure;

FIGS. 5A and 5B are block diagrams illustrating an electricalconfiguration of a biometric authentication device according to a thirdexample of the present disclosure; and

FIG. 6 is a block diagram illustrating an electrical configuration of abiometric authentication device according to a fifth example of thepresent disclosure.

DETAILED DESCRIPTION

Embodiments of the present disclosure will be described. A biometricauthentication device of the present disclosure relates to a thin aerialvideo authentication device with a function of displaying an aerialimage in a three-dimensional space without wearing special glasses orthe like. The user holds a living body over a position guided by anaerial image, the living body at the position is imaged by an imagingcamera, and biometric authentication is performed. Note that thedrawings referred to in the description of the following examplesinclude exaggerations and emphases for easy understanding of thedisclosure, and thus it should be noted that the drawings do notnecessarily indicate the shapes or scales of real products, directly.

Next, examples of the present disclosure will be described in detail.FIG. 2A is a schematic perspective view of a biometric authenticationdevice according to a first example of the present disclosure, and FIG.2B is a side view thereof. A biometric authentication device 100 of thepresent example displays an aerial image P1 at a position of a height Dfrom a surface of a casing such as a housing. The user holds a palm H tomatch the aerial image P1 at the height D, the palm H at the height D isimaged by the built-in imaging camera, and personal authentication isperformed. The user can intuitively hold the palm H by visuallyrecognizing the aerial image P1. The height D is a distance at which thepalm H can be clearly imaged by the imaging camera. The living body tobe authenticated is not particularly limited, and is, for example, afingerprint, a vein, or the like of a palm or a finger.

FIG. 3 is a schematic cross-sectional view illustrating a configurationof the biometric authentication device 100 illustrated in FIG. 2A takenalong line X-X. As illustrated in the drawing, the biometricauthentication device 100 includes a light source 110, a polarizationfilter 120, a light guide layer 130, a retroreflective layer 140, apolarization beam splitter 150, and an imaging camera 160.

The light source 110 is disposed in the vicinity of a side portion 132of the light guide layer 130, emits light having a constant emissionangle (or radiation angle) toward the light guide layer 130, anduniformly irradiates the inside of the light guide layer 130 with light.The light source 110 is not particularly limited, but for example, alight emitting element such as a light emitting diode or a laser diodecan be used. The number of light emitting elements is not particularlylimited.

The polarization filter 120 is provided between the light source 110 andthe incident surface (side portion) 132 of the light guide layer 130.The polarization filter 120 is, for example, a polarizing film or a DBEF(reflective polarizing element), and converts light from the lightsource 110 into a certain polarization state (for example, linearlypolarized light). The polarization filter 120 is particularly useful ina case where the light from the light source 110 is unpolarized, but maybe omitted when the light from the light source 110 is polarized.

The light guide layer 130 corresponds to a transparent optical member ina tabular shape or a film shape, having a flat upper face, a flat bottomface, and side faces connecting the upper face and the bottom face. Theplane shape of the light guide layer 130 is not particularly limited andthus is, for example, rectangular. For the light guide layer 130, apublicly known light guiding layer, for example, made of glass, anacrylic plastic, a polycarbonate resin, or a cycloolefin-based resin canbe used.

A light diffusion unit 136 for diffusing or scattering light in thevertical direction is formed on the bottom portion or the bottom surface134 of the light guide layer 130. The light diffusion unit 136 generatesa design (original image) of the aerial image P1, and in this example,the light diffusion unit 136 generates a design of a palm, which is aliving body to be authenticated. The light diffusion unit 136 is formed,for example, by processing a fine structure such as a dot pattern, bylaser processing or printing, on the bottom surface of the light guidelayer 130.

The retroreflective layer 140 is formed on the bottom surface side ofthe light guide layer 130. The retroreflective layer 140 is an opticalmember that reflects light in the same direction as the incident light.The retroreflective layer 140 is not particularly limited inconfiguration, and thus, for example, includes a prism typeretroreflective element, such as a triangular pyramid typeretroreflective element or a full-cube corner type retroreflectiveelement, or a bead type retroreflective element. A protective film, aretardation film (for example, λ/4 film), or the like may be interposedbetween the light guide layer 130 and the retroreflective layer 140.

The polarization beam splitter 150 is disposed on the upper surface sideof the light guide layer 130. The polarization beam splitter 150 is anoptical element that transmits a part of incident light and reflects apart of the incident light, and is a polarization separation elementthat divides the incident light into a p-polarization component and ans-polarization component. For example, the polarization beam splitter150 transmits part of light in a certain polarization state and reflectspart of the light.

A light L1 incident from the side portion 132 of the light guide layer130 travels inside while being totally reflected by, for example, theupper surface and the bottom surface of the light guide layer 130, whilea part of the light L2 is diffused and scattered in the verticaldirection by the light diffusion unit 136, and the diffused andscattered light L2 is transmitted through the upper surface of the lightguide layer 130 and reflected by the polarization beam splitter 150. Apart L3 of the light reflected by the polarization beam splitter 150 isreflected by the retroreflective layer 140 in the same direction as theincident light, and a part of the light L4 reflected by theretroreflective layer 140 is transmitted through the polarization beamsplitter 150 to generate the aerial image P1. The aerial image P1 isobtained by floating a design (original image) generated by the lightdiffusion unit 136 in the air in a posture as it is, the aerial image P1is generated at a position of a height D from the polarization beamsplitter 150, and the height D is a position symmetrical to the lightdiffusion unit 136 with respect to the plane of the polarization beamsplitter 150.

In addition to the function of displaying the aerial image P1 at theposition of the height D, the biometric authentication device 100 of thepresent example has a function of imaging the palm H of the usersuperimposed on the height of the aerial image P1 as illustrated inFIGS. 2A and 2B. In order to obtain an imaging function, an opening 142penetrating the retroreflective layer 140 is formed, and the imagingcamera 160 captures an image of the palm H via the opening 142. Theposition and size of the opening 142 are selected so that the entirepalm H can be imaged by the imaging camera 160. Furthermore, the focalpoint of the imaging camera 160 is adjusted to the vicinity of theheight D of the aerial image P1. For example, when the height of theaerial image P1 is D, the focal length F of the imaging camera 160 isadjusted to F≈2D.

When the user's palm H is placed in the air to overlap the aerial imageP1, the imaging camera 160 images the palm H. Although the imagingtiming is not particularly limited, for example, the aerial image P1 maybe automatically captured within a certain period after being displayed,or the user may give an instruction of imaging by the imaging camera160, or in a case where the biometric authentication device is equippedwith a distance sensor, a proximity sensor, or the like, the imagingcamera 160 may capture an image in response to detection of the livingbody by the sensor. Image data captured by the imaging camera 160 isused for personal authentication of the user.

As described above, according to the present example, since the aerialimage P1 representing the design to be biometrically authenticated isdisplayed in the air to guide the position at which the living body isto be held, the user can intuitively place the living body such as thepalm or the finger on the height D of the aerial image P1.

Next, a second example of the present disclosure will be described. FIG.4 is a schematic cross-sectional view of a biometric authenticationdevice 100A according to the second example of the present disclosure,and the same components as those of the first example are denoted by thesame reference numerals.

As described in the first example, the imaging camera 160 images thepalm H through the opening 142, but a part L5 of the light reflected bythe polarization beam splitter 150 becomes stray light through theopening 142 and is taken into the imaging camera 160. When the straylight is captured, the SN ratio decreases, the image data is adverselyaffected, and the accuracy of the biometric authentication decreases.

Therefore, in the second example, the polarization filter 170 isinterposed between the opening 142 and the imaging camera 160 so thatthe reflected light L5 from the polarization beam splitter 150 is nottaken into the imaging camera 160. The polarization filter 170 has apolarization state that suppresses transmission of the reflected lightL5 from the polarization beam splitter 150. For example, thepolarization direction of the polarization filter 170 is different fromthe polarization direction of the polarization beam splitter 150, andfor example, the polarization direction of the polarization filter 170is orthogonal to the polarization direction of the polarization beamsplitter 150. As a result, unnecessary reflected light L5 from thepolarization beam splitter 150 is prevented from being taken into theimaging camera 160, and deterioration in quality of image data of theliving body captured by the imaging camera 160 is prevented.

Next, a third example of the present disclosure will be described. FIG.5A is a block diagram illustrating an electrical configuration of abiometric authentication device 100B according to the third example. Thebiometric authentication device 100B includes a light source drive unit200 that drives a light source 110, an imaging camera 210 (imagingcamera 160 in FIGS. 3 and 4 ) that captures an image of the living bodyin the vicinity of the aerial image P1, and a control unit 220 thatcontrols each unit. In some embodiments, the control unit 220 and/orlight source drive unit 200 may be implemented with circuitry, acontroller, a hardwired processor, and/or a processor configured toexecute instructions stored in a memory.

In the third example, as illustrated in FIG. 5B, the control unit 220causes the light source 110 to be repeatedly turned on and off at aconstant cycle via the light source drive unit 200, and causes theimaging camera 210 to image the living body during a period in which thelight source 110 is turned off. For example, while the light source 110is turned off between a time t1 and a time t2, the imaging camera 210 iscaused to capture the image of the living body.

In this manner, the display of the aerial image P1 and the imaging ofthe imaging camera are time-divisionally controlled, and the living bodyis imaged during the period in which the reflected light L5 from thepolarization beam splitter 150 does not occur, whereby it is possible toprevent stray light from being taken into the imaged image data. In thethird example, the polarization filter 170 used in the second example isnot necessarily required, but the polarization filter 170 may beinterposed.

Next, a fourth example of the present disclosure will be described. Inthe fourth example, in a case where an infrared camera is used tocapture an image of a vein or the like of a palm or the like, a visiblelight filter is used together with the polarization filter 170 used inthe second example or instead of the polarization filter 170. Thevisible light filter cuts visible light, prevents visible light fromentering the infrared camera, and transmits infrared light or the likehaving a wavelength other than visible light.

According to the present example, by interposing the visible lightfilter at the position matching the opening 142, it is possible toprevent visible light from being reflected in the infrared camera,increase the S/N of the infrared image data by cutting visible lightnoise, and improve the biometric authentication accuracy.

Next, a fifth example of the present disclosure will be described. Asillustrated in FIG. 6 , a biometric authentication device 100C of thepresent example includes a sensor 230 that detects approach or distanceof the living body and an output unit 240 in addition to theconfiguration of FIGS. 5A and 5B. In response to the sensor 230detecting that the living body approaches the height D of the aerialimage P1, the control unit 220 causes the imaging camera 210 to capturean image of the living body. Then, in response to the end of the imagingof the living body by the imaging camera 210, a sound (for example, beepsound) indicating the end of the imaging is output from the output unit240. As a result, the user can know that imaging for authentication ofthe living body has been performed, and can return the palm H to theoriginal position. In some embodiments, the output unit 240 may beimplemented as a speaker associated with circuitry, a controller, ahardwired processor, and/or a processor configured to executeinstructions stored in a memory.

Furthermore, as another aspect, in order to notify the user of the endof imaging by the imaging camera 210, the control unit 220 may blink thelight source 110 via the light source drive unit 200 or turn on thelight source 110 with brightness or color different from normalbrightness or color. For example, in the case of urging imaging for theliving body, the aerial image P1 may be displayed in blue, and theaerial image P1 may be displayed in green when the imaging is completed.

The biometric authentication device according to the present example canbe applied to user input of any equipment, and can be applied to, forexample, a computer device, in-vehicle electronic equipment, an ATM at abank or the like, a ticket purchasing machine at a station or the like,or an input button for an elevator.

While there has been illustrated and described what is at presentcontemplated to be preferred embodiments of the present disclosure, itwill be understood by those skilled in the art that various changes andmodifications may be made, and equivalents may be substituted forelements thereof without departing from the true scope of thedisclosure. In addition, many modifications may be made to adapt aparticular situation to the teachings of the disclosure withoutdeparting from the central scope thereof. Therefore, it is intended thatthis disclosure not be limited to the particular embodiments disclosed,but that the invention will include all embodiments falling within thescope of the appended claims.

What is claimed is:
 1. A biometric authentication device with a functionof displaying an aerial image using retroreflection, the biometricauthentication device comprising: a light guide layer on which a designfor the aerial image is formed; a light source that irradiates the lightguide layer with light; a polarization beam splitter disposed on oneprincipal surface side of the light guide layer; a retroreflective layerdisposed on a side of the other principal surface of the light guidelayer, the other principal surface facing the one principal surface; andan imaging unit that captures an image of a living body in the vicinityof a region where the aerial image is displayed via an opening formed inthe retroreflective layer, wherein the biometric authentication deviceperforms biometric authentication based on the image captured by theimaging unit.
 2. The biometric authentication device according to claim1, wherein a polarization filter having a polarization directiondifferent from that of the polarization beam splitter is provided at aposition matching the opening.
 3. The biometric authentication deviceaccording to claim 2, wherein the polarization direction of thepolarization filter is orthogonal to a polarization direction of thepolarization beam splitter.
 4. The biometric authentication deviceaccording to claim 1, wherein the imaging unit captures an image of aliving body at a time when the light source is turned off.
 5. Thebiometric authentication device according to claim 4, wherein display ofthe aerial image and imaging of the imaging unit are time-divisionallycontrolled.
 6. The biometric authentication device according to claim 1,wherein the imaging unit includes an infrared camera, and a visiblelight filter that shields visible light is provided at a positionmatching the opening.
 7. The biometric authentication device accordingto claim 1, wherein the aerial image is generated at a positionsymmetrical to the design with respect to a surface of the polarizationbeam splitter, and a focal point of the imaging unit is adjusted to aposition of the aerial image.
 8. The biometric authentication deviceaccording to claim 1, further comprising: an output unit that notifiesthe user that imaging by the imaging unit has ended.
 9. The biometricauthentication device according to claim 1, wherein the living body is afingerprint or a vein.